Adding spark-comminuted zinc to tobacco-smoke filters

ABSTRACT

The invention concerns a method and apparatus for improving the filtration properties of fibrous, filamentary and sheet tobacco smoke filtering material. The method consists in treating the said material with a finely divided zinc-containing powder produced by a high-energy comminution process carried out under water. The powder is advantageously a powder produced by electric-spark erosion action between two zinc electrodes submerged in water.

D United States Patent {1113,560,697

[72} inventor Thomas William Charles Tolman [50] Field of Search 2l9/69M, Southampton, England 69V, 50, 68, 70; l31/9, 10, 88, 196, 207,261, 264, [2!] Appl No. 750,656 265, 266 [22] Filed Aug. 6, 1968 45Patented Feb. 2, 1971 1 References Cited [73] Assignee Brown andWilliamson Tobacco UNITED STATES PATENTS corporatim 1,564,500 12/ 1925Van de Voorde i3 l/261UX Louisville, Ky. a corpomfion 0 Delaware PrimaryExammerR F. Staubly [32] priority Aug 9, 1967 Attorneyl(ane, Dalsimer,Kane, Sullivan and Kurucz [33] Great Britain [31] 36520/67 ABSTRACT: Theinvention concerns a method and apparatus [54] ED ZINC To for improvingthe filtration properties of fibrous, filamentary 7 Claims 2 D and sheettobacco smoke filtering material. The method conrawmg sists in treatingthe said material with a finely divided zinc- [52] U.S.Cl....- 219/69,containing powder produced by a high-energy comminution 131/10, 13 1I26] process carried out under water. The powder is ad- (51] Int. Cl823p i/08, vantageously a powder produced by electric-spark erosion ac-A24f 25/00 tion between two zinc electrodes submerged in water.

ADDING SPARK-COMMINUTED ZINC TO TOBACCO- SMOKE FILTERS Many forms offilter for tobacco smoke consist of filamenta- 1 ry or sheet materialcapable of removing the particulate phase by nonnal filter mechanism.Commonly, additional materials are incorporated into such filters toimprove their effectiveness by removing a proportion of the vapor phase,or specific substances therefrom. Such materials are usually substanceswhich can remove the less pleasant constituents which are present in thetobacco smoke and which have an adverse effeet on the taste of thefiltered smoke. Of these less pleasant constituents of tobacco smoke,the presence of the more volatile acidic compounds may be undesirable,especially hydrogen sulfide and hydrogen cyanide.

An object of the present invention is to provide means whereby hydrogensulfide and hydrogen cyanide can be largely removed from the smoke ofburning tobacco.

According to the invention, fibrous, filamentary or sheet tobacco smokefiltering material is treated with a finely divided zinc-containingpowder produced by a high-energy comminution process carried out underwater.

Preferably, the powder is produced by electric-spark action between twozinc electrodes submerged in water. In this case, the finely dividedzinc-containing powder may be obtained initially as a grey-blacksuspension in distilled water which, on standing, changes colour tobecome light grey. This powder may contain about 90 percent zinc.

The powder is applied to the filtering material in the fonn of theaqueous suspension, by dipping, spraying or coating, to give a finalincrease in weight after drying of up to percent based on the originalweight of the said material. Quite small additions are efieetive, butpractical difficulties arise if the addition exceeds 10 percent.Preferably, the addition is such as to give an increase in weight offrom 2 percent to 5 or 6 percent approximately.

One manner of preparing the aqueous suspension of finely dividedzinc-containing powder will now be more fully described by way ofillustration. In the accompanying draw- FIG. I is a diagram of asuitable arrangement of spark-erosion apparatus used for preparing thesuspension, and

FIG. 2 a circuit diagram for this apparatus.

Referring to FIG. I, the apparatus comprised a stationary zinc electrodeI in the form of a large flat disc and a movable zinc electrode 2 in theform of a slender rod clamped to the soft iron core 3 of a solenoid 4.The two electrodes 1, 2 were arranged mutually in contact 2 cm. belowthe surface of a dish 5 containing distilled water of relatively lowconductivity. The movable electrode 2 and core 3 were counterbalanced byan adjustable weight 6 to such an extent that a small attractive forceby the solenoid 4 on the core would suffice to separate the twoelectrodes.

The circuit, FIG. 2, for the electrodes 1, 2 and solenoid 4 was suppliedwith direct current from a source 7 of alternating current at l40 voltsthrough a full-wave rectifier 8, the electrade 2 being connected to thepositive side. An S-microfarad capacitor 9 was connected across theelectrodes 1, 2 which were effectively, in series with the saidcapacitor. For adjustably controlling the current flow through thesolenoid 4, a variable-series resistor 10 and variable shunt resistorsll,l2, of 200, I55 and 45 ohms respectively, were provided.

When the circuit was switched on, current flowed by way of theelectrodes I, 2 through the solenoid 4. The resultant attraction of thecore 3 lifted the movable electrode 2, interrupting contact between thetwo electrodes. The capacitor 9 rapidly became charged to its dischargepotentiaiand, at a critical maximum separation of the electrodes I, 2,discharge across them, causing a spark to be produced. In the meanwhile,due to the separation of the electrodes, the solenoid becamesubstantially deenergized, so that the core 3 was no longer attractedand the electrode 2 returned towards contact with the electrode 1.Discharge from the capacitor 9 ceased and the solenoid was reencrgizedand the electrodes 1,2 reseparated, the cycle being repeatedcontinuously and rapidly to produce a continuous rapid succession oferosive sparks between the electrodes.

During the first few seconds of operation, a brown colloidal solutionwas formed in the dish 5, which changed during continued operation to adark grey/black suspension. On subsequent standing, the particles in thesuspension changed colour to become light grey. Analysis of these lightgrey particles showed that they contained 88 percent by weight of zinc.If it is assumed that the colour change is brought about by theformation of zinc hydroxide, this analysis corresponds to a compositionfor the particles of approximately percent zinc and 25 percent zinchydroxide. The particles proved to be irregularly shaped aggregates ofsize ranging from 5 to 50 microns. The components of the aggregates wereof size from 0.5 to 1 micron.

The following examples illustrate the effect of the addition of asuspension of zinc-containing particles produced by the spark-erosionprocess to filters of paper and cellulose acetate.

EXAMPLE I A suspension of light grey particles obtained in theabovedescribed manner was sprayed onto tobacco smoke filtering paper ofthe kind well-known as "Myria" paper to give a final increase in weight,after drying, of 0.5 percent, calculated on the original weight of thepaper.

The treated paper was formed into filter rods of cigarette diameter andcut into filter tips each of i5 mm. length.

EXAMPLE II I The procedure of example I was repeated, except that aquantity of the suspension sufficient to give a final increase in weightof 1 percent was applied.

EXAMPLE m The procedure of example I was repeated except that thesuspension was applied so as to give an increase in weight of 2.5percent.

EXAMPLE IV The procedure of example I was repeated except that thesuspension was applied so as to give an increase in weight of 5.0percent.

EXAMPLE V The procedure of example I was repeated except that thesuspension was applied so as to give an increase in weight of 10.0percent.

Filter tips prepared as in the above examples were attached tocigarettes and smoked, in comparison with cigarettes without filtertips, using an engine which provided one puff per minute of 2 secondsduration and 35 cc. volume. The smoke collected was analyzed and theascertained amounts of hydrogen sulfide and hydrogen cyanide removed bythe treated filters are shown in Table I below.

Filtration ellieiency for 15 Pressure drop, mm. filter, percent em.water gauge (at air [low of Hydrogen Hydrogen Example 1,050 ce./min.)sulphide cyanide EXAMPLE VI A continuous tow of cellulose acetatefilaments of filament denier 5 and total denier 72.000 was sprayed withan aqueous suspension of zinc-containing particles prepared on acommercial scale by the spark-erosion process. The particles comprised20 percent of the total weight of the suspension. The treated tow wasfed to a conventional filter-rod making machine. by which it was formedinto rods. The rods were dried at 70 F. for 48 hours and conditioned ina cabinet maintained at 70 F. and 60 percent relative humidity.

On analysis, the rods were found to contain 2.3 percent by weight ofzinc.

EXAMPLE Vll Filter rods were prepared as in example Vl except that theaddition of particles was such that the rods contained 4.6 percent ofzinc.

EXAMPLE Vlll TABLE II Filtration eflicieney for Pressure drop, mm.length, percent cm. water gauge (at air flow of Hydrogen HydrogenExample 1,050 cc./m.in.) sulphide cyanide The flavour of the smoke wasnot found to be adversely affected by the additions made to thefiltering materials in any of examples I to Vlll.

lclaim:

l. A method of improving the filtration properties of tobacco smokefiltering material of the group consisting of fibrous, filamentary andsheet filtering material, comprising treating the said material with afinely divided. zinc-containing powder produced by a high-energycomminution process carried out under water.

2. A method according to claim 1, wherein the powder is produced byelectric-spark erosion action between two zinc electrodes submerged inwater.

3. A method according to claim 1, wherein the filtering material istreated with the zinc-containing powder in the form of an aqueoussuspension and is dried.

4. A method according to claim 1, wherein the filtering material istreated to give a final increase in weight of up to 10 percent withrespect to the original weight of the said material.

5. A method according to claim 1, wherein the filtering material istreated to give a final increase in weight of from,2 to 5 percent withrespect to the original weight of the said material.

6. A method of improving the filtration properties of tobacco smokefiltering material comprising treating the said material with a minoramount of a finely divided zinc-contain ing powder, said powder beingproduced by a high energy comminution process carried out under waterand then forming a filter element from said treated filtering materialwhereby said filter element is adapted to be attached to a smokearticle.

7. A tobacco smoke filter element made by the methodof claim 6.

1. A method of improving the filtration properties of tobacco smokefiltering material of the group consisting of fibrous, filamentary andsheet filtering material, comprising treating the said material with afinely divided zinc-containing powder produced by a high-energycomminution process carried out under water.
 2. A method according toclaim 1, wherein the powder is produced by electric-spark erosion actionbetween two zinc electrodes submerged in water.
 3. A method according toclaim 1, wherein the filtering material is treated with thezinc-containing powder in the form of an aqueous suspension and isdried.
 4. A method according to claim 1, wherein the filtering materialis treated to give a final increase in weight of up to 10 percent withrespect to the original weight of the said material.
 5. A methodaccording to claim 1, wherein the filtering material is treated to givea final increase in weight of from 2 to 5 percent with respect to theoriginal weight of the said material.
 6. A method of improving thefiltration properties of tobacco smoke filtering material comprisingtreating the said material with a minor amount of a finely dividedzinc-containing powder, said powder being produced by a high energycomminution process carried out under water and then forming a filterelement from said treated filtering material whereby said filter elementis adapted to be attached to a smoke article.
 7. A tobacco smoke filterelement made by the method of claim 6.